1. Field of the Invention
The invention relates to a thin film magnetic head and, particularly, to a thin film magnetic head characterized by the construction of its plating base layer for providing a magnetic pole core of a thin film magnetic head of an induction type constituting a hard disc drive (HDD) with a high saturation magnetic flux density.
2. Description of the Related Art
Recent hard disc drives, which are external storage devices for computers, have an increasing recording density, and comprise a magnetic head with small elements. Also, recent recording mediums have an increasing coercive force. Under the circumstances, a magnetic head capable of adequately writing records to such a recording medium having a high coercive force are demanded.
In inductive thin film magnetic heads, a thin film of Ni-Fe alloy is commonly used as a material for a write magnetic pole. Most of the write magnetic poles have a two-layer structure of a layer of Ni50Fe50, i.e., 50 permalloy, provided on a read gap and having a saturation magnetic flux density BS of the order of 1.5 teslas (T) and a thickness of the order of 1 micrometer, and a layer of Ni80Fe20, i.e., 80 permalloy, laminated thereon and having a thickness of 1 to 4 micrometers. This is for the sake of ensuring sufficient recording properties at a strong magnetic field by placing a magnetic material having a saturation magnetic flux density BS higher than 80 permalloy near an upper magnetic pole gap which is the point for finally writing on a recording medium.
A practical magnetic pole core, which is made up entirely of 50 permalloy having a BS nearly equal to 1.5 T, is known. However, since 50 permalloy has a large magnetostriction, there is a possibility that the 50 permalloy material is strained during processing, and this degrades the magnetic properties of a magnetic pole core.
Referring to FIGS. 6A to 6C, a process for manufacturing a conventional writing thin film magnetic head is described.
As shown in FIG. 6A, a plating base layer 32 of Ni80Fe20 and a lower magnetic pole layer 33 of Ni80Fe20 are successively formed on a TiC substrate 31 provided with an Al2O3 film (not shown) (also called Al2O3xe2x80x94TiC substrate). The surface of the magnetic pole layer 33 is then planarized, and a write gap layer 34 consisting of Al2O3 or the like is provided thereon by a sputtering process. There is a case where the write gap layer 34 is subsequently patterned together with the lower magnetic pole layer 33 of Ni80Fe20 and, accordingly, they are depicted to have the same width in the drawing.
Subsequently, in a region which is not shown in FIG. 6A, a first interlayer insulation film of a resist material or the like, a coil in a shape of horizontal spiral on the first interlayer insulation film, and a second interlayer insulation film of a resist material or the like on the coil are successively formed, the coil being provided at both ends thereof with an electrode.
A further base layer 35 of Ni80Fe20 having a thickness of, for example, 0.1 micrometer is then formed on the write gap layer 34 by a sputtering process, as shown in FIG. 6A.
Referring to FIG. 6B, a patterned resist layer 36 is then formed and, using the patterned resist layer 36 as a plating frame, an Ni50Fe50 layer 37 having a thickness of, for example, 1 micrometer and an Ni80Fe20 layer 38 having a thickness of, for example, 2.0 micrometers are successively formed by a plating process, to provide an upper magnetic pole 39.
Referring to FIG. 6C, after the removal of the resist layer 36 (FIG. 6B), exposed portions of the plating base layer 35 of Ni80Fe20, which are shown by the broken lines in FIG. 6C, are removed by ion milling using Ar ions 40.
Subsequently, an Al2O3 film, as a protective film, is provided on the entire face of the substrate 31 having a laminate structure of formed layers, although not shown in the drawing, and the substrate is cut and subjected to a slider making process which includes grinding for adjusting lengths of write poles, i.e., a gap depth, and polishing, to thereby produce a basic construction of a thin film magnetic head.
When the thin film magnetic head obtained as described above referring to FIGS. 6A to 6C was used to write a magnetic recording medium having a coercive force HC of 3500 oersteds (Oe), it was found that an overwrite value was xe2x88x9227 dB.
However, since an overwrite value is generally regarded as being practical when it is xe2x88x9230 dB or lower, the conventional thin film magnetic head as described above was not appropriate as a thin film magnetic head for a recording medium of high recording density having a coercive force HC of the order of 3500 Oe.
Thus, with the development of recent recording mediums having a higher coercive force, it is necessary to use a material having a higher saturation magnetic flux density BS for an upper magnetic pole core, or for an upper magnetic pole core and a lower magnetic layer, constituting an inductive thin film magnetic head, and with the need of such a higher saturation magnetic flux density, it has been recognized that a magnetic thin film for the upper magnetic pole core and the lower magnetic layer must have a BS nearly equal to 2.0 T at a portion at which a magnetic flux is most concentrated.
As a magnetic thin film material meeting such a need of higher saturation magnetic flux density, CoNiFe materials were developed (Japanese Patent Application No. 2000-7487, which has not been published at the filing of the present application). The CoNiFe material has magnetic properties superior to those of 80 permalloy and 50 permalloy. For example, Co64Ni12Fe24 has a saturation magnetic flux density BS nearly equal to 2 T, and can provide a thin magnetic head having a head magnetic field which is larger than that of conventional thin film magnetic head.
Nevertheless, a film of such a CoNiFe material, which is formed by an electroplating process, has an internal stress, which is distributed in the plane of the formed film, of about 0.5 to 10xc3x971010 dyn/cm2, which is large compared to 80 permalloy and 50 permalloy, and when it is formed into a film having a thickness of micron-order, it will give rise to a problem that the formed film is prone to peel. Incidentally, a Co64Ni12Fe24 film has an internal stress of about 7xc3x971010 dyn/cm2.
When a magnetic thin film is peeled, the peeled magnetic thin film, which represents a metal piece, damages other part or parts of a magnetic head, or leads to the generation of dust in another process, and causes trouble to an apparatus for manufacturing a magnetic head. Consequently, it has been difficult to use a CoNiFe material as a magnetic material for a thin film magnetic head.
Thus, the invention aims to enhance a writing capacity of a thin film magnetic head by the use of a magnetic film of high saturation magnetic flux density having a small thickness. In particular, a CoFeNi base layer formed of a sputtered or evaporated film is formed in contact with a gap layer of the thin film magnetic head to overcome the problems discussed above directed to peeling of the magnetic head.
A thin film magnetic head according to the invention is characterized by comprising a base layer, which makes up an upper magnetic pole of the thin film magnetic head, made of a magnetic film having a saturation magnetic flux density of 1.2 teslas (T) or larger, more preferably 1.9 teslas or larger. Thus, the invention provides a thin film magnetic head comprising a substrate, a lower magnetic pole provided on the substrate, a write gap layer located on the lower magnetic pole, and an upper magnetic pole located on the gap layer, the upper magnetic pole including a plating base layer in contact with the gap layer, wherein the plating base layer of the upper magnetic pole is made of a magnetic film having a saturation magnetic flux density of 1.2 T or larger, more preferably 1.9 teslas or larger.
Preferably, the thin film magnetic head of the invention further comprises a thin magnetic film having a saturation magnetic flux density of 1.2 T or larger, more preferably 1.9 teslas or larger, between the lower magnetic pole and the write gap layer.
Preferably, at least one of the base layer and the thin magnetic film located between the lower magnetic pole and the write gap layer is formed of a magnetic material of alloy containing one or more of elemental Co, Ni, and Fe.
Preferably, at least one of the base layer and the thin magnetic film located between the lower magnetic pole and the write gap layer is formed of a sputtered or evaporated film.
Preferably, at least one of the base layer and the thin magnetic film located between the lower magnetic pole and the write gap layer has a thickness of 0.05 micrometer or more.
Preferably, the upper magnetic pole comprises an electroplated film having a saturation magnetic flux density of 1.5 T or larger located on the base layer.
Preferably, the electroplated film is formed of a magnetic film having a higher saturation magnetic flux density and a magnetic film having a lower saturation magnetic flux density, the magnetic film having a higher saturation magnetic flux density being located closer to the base layer.
The invention can provide a magnetic storage device using the thin film magnetic head according to the invention, the magnetic storage devise having an enhanced recording capacity and being capable of adequately writing record to a recording medium having a high coercive force.